[Alaska Jim]

I think it is possible that you have a rod bearing going bad by what you describe. you could be lucky and just have a piece of carbon come loose, and caught in there. I have had this happen on a chevy 454 once. I would have sworn it had a bad rod, but tore it down , only to find A large chunk of carbon had come loose and would not pass though the valves and was hitting the top of the piston. If you have a bad rod bearing, it will most likely need to have the crank turned and the rod replaced or resized. usually if a rod bolt "stretches" it breaks. either way it will need new bearing and the crank turned.